1. Field of the Invention
The present invention relates to a semiconductor device including a capacitor having a dielectric film formed of a dielectric material having a high dielectric constant or a ferroelectric material, and a method for fabricating the same.
2. Description of the Related Art
Recently, as functions of consumer electric and electronic appliances have been more and more advanced along with higher processing rates and lower power consumption of microcomputers, the size of semiconductor devices used in the microcomputers has rapidly decreased. This has been accompanied by the serious problem of unnecessary radiation, which is electromagnetic wave noise generated from the electric and electronic appliances.
In order to reduce the unnecessary radiation, technologies for incorporating a capacitor having a large capacitance including a dielectric film formed of a dielectric material having a high dielectric constant (hereinafter, referred to as a “high dielectric constant material film”) into a semiconductor device have been the target of attention. Furthermore, in accompaniment of higher integration dynamic RAMs (DRAMs), technologies for using a high dielectric constant material film in the capacitor, in lieu of a silicon oxide film and a silicon nitride film which are conventionally used, have been widely studied.
Furthermore, in order to realize non-volatile RAMs which are operable at lower voltages and provide higher read/write rates, ferroelectric material films exhibiting spontaneous polarization have been actively studied.
The most important point in realizing semiconductor devices having the above-described features is to develop a structure which permits multi-layered interconnects without deteriorating the characteristics of the capacitor and a method for fabricating such a structure.
Hereinafter, an exemplary conventional method for fabricating a semiconductor device 500 will be described with reference to FIGS. 10A through 10E (cross-sectional views).
As shown in FIG. 10A, an integrated circuit 4 and a device isolating insulating layer 5 are formed on a supporting substrate 1. The integrated circuit 4 includes a MOS field effect transistor (MOSFET) having a gate electrode 2, and source and drain regions 3. An insulating layer 6 is formed on the resultant laminate. A film which will act as a lower electrode 7 of a capacitor 10 is formed on the insulating layer 6 by sputtering or electron beam deposition. Then, a dielectric film 8 made of a high dielectric constant material film or a ferroelectric material film is formed on the film to act as the lower electrode 7 by metal organic deposition, metal organic chemical vapor deposition, or sputtering. Subsequently, a film which will act as an upper electrode 9 is formed on the dielectric film 8 by sputtering or electron beam deposition. Then, the layers 7, 8 and 9 are patterned into desirable patterns, thereby forming a capacitor 10.
Next, as shown in FIG. 10B, a first interlayer insulating film 11 is formed on the insulating layer 6 so as to cover the capacitor 10. Contact holes 12 are formed so as to run through the first interlayer insulating film 11 and reach, respectively, the lower electrode 7 and the upper electrode 9 of the capacitor 10. Contact holes 13 are also formed so as to run through the first interlayer insulating film 11 and the insulating layer 6 and reach, respectively, the source and drain regions 3. Conductive layers are formed on the first interlayer insulating film 11 and in the contact holes 12 and 13 by sputtering or the like, and patterned into desired patterns. Thus, first interconnects 14 for electrically connecting the integrated circuit 4 and the capacitor 10 are formed. The first interconnects 14 are then subjected to a thermal treatment.
As shown in FIG. 10C, a second interlayer insulating film 15 are formed on the resultant laminate so as to cover the first interconnects 14. The second interlayer insulating film 15 is formed by substantially planarizing, by etch-back, a silicon oxide film formed by plasma CVD using tetraethyl orthosilicate (TEOS) (hereinafter, referred to as a “plasma TEOS film”) or a laminate including the above-described plasma TEOS film and a silicon-on-glass (SOG) film.
As shown in FIG. 10D, contact holes 16 are formed so as to run through the second interlayer insulating film 15 and reach the first interconnects 14. Second interconnects 17 are selectively formed on the second interlayer insulating film 15 and in the contact holes 16 so as to be electrically connected to the first interconnects 14. The second interconnects 17 are then subjected to a thermal treatment.
As shown in FIG. 10E, a passivation layer 18 is formed so as to cover the second interconnects 17 on the resultant laminate. Thus, the semiconductor device 500 is fabricated.
In the above-described method for fabricating the semiconductor device 500, the second interlayer insulating film 15 needs to be formed so as to have no step and a flat top surface and thus have a sufficient step coverage property. The reason for this is that, when the second interlayer insulating film 15 has a step, the second interconnects 17 to be formed thereon may disadvantageously be disconnected at the step. Accordingly, the conventional second interlayer insulating film 15 formed of a plasma TEOS film or the like needs to have a thickness h1 (FIG. 10C) of about 1 μm or more on the first interconnects 14 above the upper electrode 9 and also have a thickness h2 (FIG. 10C) of about 2 μm or more on the first interlayer insulating film 11 on an edge of the dielectric film 8 formed of a high dielectric constant material film or a ferroelectric material film.
Generally, however, when the force per unit thickness is constant, a thicker layer results in a stronger tensile or compressive stress. Thus, when the thickness of the second interlayer insulating film 15 is as thick as above-described, a significantly strong stress is applied to the capacitor 10 provided below the second interlayer insulating film 15.
Specifically when the second interlayer insulating film 15 is formed of a plasma TEOS film, the compressive stress acting on the dielectric film 8 prevents the polarization of the dielectric material forming the dielectric film 8. As a result, the physical properties of the dielectric film 8 formed of the high dielectric constant material or ferroelectric material deteriorate.
As used herein, the term “stress” refers to a force for contracting the layer (hereinafter, referred to as a “tensile stress”) and/or a force for expanding the layer (hereinafter, referred to as a “compressive stress”).